1. Field of the Invention
The present invention relates to an optical semiconductor device such as a double-channel planer buried heterostructured (DC-PBH) semiconductor laser device.
2. Description of the Related Art
Generally, in a DC-PBH semiconductor laser device, in order to reduce a leakage current (invalid current) at a high temperature or in a high bias condition, a current blocking structure using a pnpn-type thyristor-structure has been adopted. However, in such a pnpn-type thyristor-structure, carrier recombination at a high bias condition charges up the thyristor to turn it ON (see JP-A-102583; I. Mito et al., xe2x80x9cDouble-channel Planar Buried-Heterostructure Laser Diode With Effective Current Confinementxe2x80x9d, Electronics Lett., Vol. 18, No. 22, pp. 953-954, October 1982; and Y. Sakata et al., xe2x80x9cLow Threshold and High Uniformity for Novel 1.3 xcexcm-strained InGaAsP MQW DC-PBH LD""s Fabricated by the All-Selected MOVPE Techniquexe2x80x9d, IEEE photonicsTech. Lett, Vol. 9, No. 3, pp. 291-293, March 1997).
In order to avoid the above-mentioned latch-up phenomenon in the pnpn-type thyristor-structure,a carrier recombination layer has been provided in the DC-PBH semiconductor laser device.
For example, in a first prior art semiconductor laser device (see JP-A-8-213691) including an InGaAsP active layer, a p-type InP buried layer, an n-type InP current blocking layer, a semi-insulating InP current blocking layer and an n-type InP buried layer, an InGaAsP carrier recombination is provided between the semi-insulating InP layer and the n-type InP buried layer.
In a second prior art semiconductor laser device (see JP-A-8-236858) including an InGaAsP active layer, an n-type InP current blocking layer and a p-type InP current blocking layer, an i-type InGaAsP carrier recombination layer is provided on the p-type InP current blocking layer.
In a third prior art semiconductor laser device (see JP-A-9-167874) including an InGaAsP bulk or quantum well structured active layer, a p-type InP buried layer, an n-type current blocking layer and a p-type current blocking layer, an In GaAsP carrier recombination layer is provided on the p-type InP current blocking layer.
In a fourth prior art semiconductor laser device (see JP-A-9-266349) including a multiple quantum well (MQW) active layer, a p-type InP buried layer, an n-type current blocking layer, a p-type current blocking layer and an n-type InP buried layer, an MQW carrier recombination layer is provided between the p-type InP current blocking layer and the n-type InP buried layer.
In a fifth prior art semiconductor laser device (see JP-A-10-93190) including an MQW active layer, a p-type InP current blocking layer and an n-type InP current blocking layer, an MQW carrier recombination layer is provided beneath the n-type InP current blocking layer.
In the above-described prior art semiconductor laser devices, however, since the structure of the carrier recombination layer is the same as that of the active layer, the invalid current consumed in the carrier recombination layer is increased as compensation to suppress the turning ON operation of the thyristor structure, thus increasing the consumption power at a high temperature and at a high bias condition.
It is an object of the present invention to provide an optical semiconductor device such as a semiconductor laser device capable of reducing the invalid current.
According to the present invention, in an optical semiconductor device including a semiconductor substrate, an active layer formed on the semiconductor-substrate, a pnpn-type current blocking layer formed on a side of the active layer, and a carrier recombination layer on the semiconductor substrate on the side of the active layer, a structure of the active layer is different from a structure of the carrier recombination layer. For example, the active layer is constructed by an MQW structure, and the carrier recombination layer is constructed by an i-type InGaAsP layer.